Remove exclusive backup mode

Exclusive-mode backups have been deprecated since 9.6 (when
non-exclusive backups were introduced) due to the issues
they can cause should the system crash while one is running and
generally because non-exclusive provides a much better interface.
Further, exclusive backup mode wasn't really being tested (nor was most
of the related code- like being able to log in just to stop an exclusive
backup and the bits of the state machine related to that) and having to
possibly deal with an exclusive backup and the backup_label file
existing during pg_basebackup, pg_rewind, etc, added other complexities
that we are better off without.

This patch removes the exclusive backup mode, the various special cases
for dealing with it, and greatly simplifies the online backup code and
documentation.

Authors: David Steele, Nathan Bossart
Reviewed-by: Chapman Flack
Discussion: https://postgr.es/m/ac7339ca-3718-3c93-929f-99e725d1172c@pgmasters.net
https://postgr.es/m/CAHg+QDfiM+WU61tF6=nPZocMZvHDzCK47Kneyb0ZRULYzV5sKQ@mail.gmail.com

1 files changed, 47 insertions, 206 deletions

diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 2752be63c10..b61ae6c0b4a 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -39,13 +39,13 @@
 #include "utils/tuplestore.h"
 
 /*
- * Store label file and tablespace map during non-exclusive backups.
+ * Store label file and tablespace map during backups.
  */
 static StringInfo label_file;
 static StringInfo tblspc_map_file;
 
 /*
- * pg_start_backup: set up for taking an on-line backup dump
+ * pg_backup_start: set up for taking an on-line backup dump
  *
  * Essentially what this does is to create a backup label file in $PGDATA,
  * where it will be archived as part of the backup dump.  The label file
@@ -57,105 +57,44 @@ static StringInfo tblspc_map_file;
  * GRANT system.
  */
 Datum
-pg_start_backup(PG_FUNCTION_ARGS)
+pg_backup_start(PG_FUNCTION_ARGS)
 {
 	text	   *backupid = PG_GETARG_TEXT_PP(0);
 	bool		fast = PG_GETARG_BOOL(1);
-	bool		exclusive = PG_GETARG_BOOL(2);
 	char	   *backupidstr;
 	XLogRecPtr	startpoint;
 	SessionBackupState status = get_backup_status();
+	MemoryContext oldcontext;
 
 	backupidstr = text_to_cstring(backupid);
 
-	if (status == SESSION_BACKUP_NON_EXCLUSIVE)
+	if (status == SESSION_BACKUP_RUNNING)
 		ereport(ERROR,
 				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
 				 errmsg("a backup is already in progress in this session")));
 
-	if (exclusive)
-	{
-		startpoint = do_pg_start_backup(backupidstr, fast, NULL, NULL,
-										NULL, NULL);
-	}
-	else
-	{
-		MemoryContext oldcontext;
-
-		/*
-		 * Label file and tablespace map file need to be long-lived, since
-		 * they are read in pg_stop_backup.
-		 */
-		oldcontext = MemoryContextSwitchTo(TopMemoryContext);
-		label_file = makeStringInfo();
-		tblspc_map_file = makeStringInfo();
-		MemoryContextSwitchTo(oldcontext);
+	/*
+	 * Label file and tablespace map file need to be long-lived, since
+	 * they are read in pg_backup_stop.
+	 */
+	oldcontext = MemoryContextSwitchTo(TopMemoryContext);
+	label_file = makeStringInfo();
+	tblspc_map_file = makeStringInfo();
+	MemoryContextSwitchTo(oldcontext);
 
-		register_persistent_abort_backup_handler();
+	register_persistent_abort_backup_handler();
 
-		startpoint = do_pg_start_backup(backupidstr, fast, NULL, label_file,
-										NULL, tblspc_map_file);
-	}
+	startpoint = do_pg_backup_start(backupidstr, fast, NULL, label_file,
+									NULL, tblspc_map_file);
 
 	PG_RETURN_LSN(startpoint);
 }
 
-/*
- * pg_stop_backup: finish taking an on-line backup dump
- *
- * We write an end-of-backup WAL record, and remove the backup label file
- * created by pg_start_backup, creating a backup history file in pg_wal
- * instead (whence it will immediately be archived). The backup history file
- * contains the same info found in the label file, plus the backup-end time
- * and WAL location. Before 9.0, the backup-end time was read from the backup
- * history file at the beginning of archive recovery, but we now use the WAL
- * record for that and the file is for informational and debug purposes only.
- *
- * Note: different from CancelBackup which just cancels online backup mode.
- *
- * Note: this version is only called to stop an exclusive backup. The function
- *		 pg_stop_backup_v2 (overloaded as pg_stop_backup in SQL) is called to
- *		 stop non-exclusive backups.
- *
- * Permission checking for this function is managed through the normal
- * GRANT system.
- */
-Datum
-pg_stop_backup(PG_FUNCTION_ARGS)
-{
-	XLogRecPtr	stoppoint;
-	SessionBackupState status = get_backup_status();
-
-	if (status == SESSION_BACKUP_NON_EXCLUSIVE)
-		ereport(ERROR,
-				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("non-exclusive backup in progress"),
-				 errhint("Did you mean to use pg_stop_backup('f')?")));
-
-	/*
-	 * Exclusive backups were typically started in a different connection, so
-	 * don't try to verify that status of backup is set to
-	 * SESSION_BACKUP_EXCLUSIVE in this function. Actual verification that an
-	 * exclusive backup is in fact running is handled inside
-	 * do_pg_stop_backup.
-	 */
-	stoppoint = do_pg_stop_backup(NULL, true, NULL);
-
-	PG_RETURN_LSN(stoppoint);
-}
-
 
 /*
- * pg_stop_backup_v2: finish taking exclusive or nonexclusive on-line backup.
- *
- * Works the same as pg_stop_backup, except for non-exclusive backups it returns
- * the backup label and tablespace map files as text fields in as part of the
- * resultset.
+ * pg_backup_stop: finish taking an on-line backup.
  *
- * The first parameter (variable 'exclusive') allows the user to tell us if
- * this is an exclusive or a non-exclusive backup.
- *
- * The second parameter (variable 'waitforarchive'), which is optional,
+ * The first parameter (variable 'waitforarchive'), which is optional,
  * allows the user to choose if they want to wait for the WAL to be archived
  * or if we should just return as soon as the WAL record is written.
  *
@@ -163,15 +102,14 @@ pg_stop_backup(PG_FUNCTION_ARGS)
  * GRANT system.
  */
 Datum
-pg_stop_backup_v2(PG_FUNCTION_ARGS)
+pg_backup_stop(PG_FUNCTION_ARGS)
 {
 #define PG_STOP_BACKUP_V2_COLS 3
 	TupleDesc	tupdesc;
 	Datum		values[PG_STOP_BACKUP_V2_COLS];
 	bool		nulls[PG_STOP_BACKUP_V2_COLS];
 
-	bool		exclusive = PG_GETARG_BOOL(0);
-	bool		waitforarchive = PG_GETARG_BOOL(1);
+	bool		waitforarchive = PG_GETARG_BOOL(0);
 	XLogRecPtr	stoppoint;
 	SessionBackupState status = get_backup_status();
 
@@ -182,51 +120,29 @@ pg_stop_backup_v2(PG_FUNCTION_ARGS)
 	MemSet(values, 0, sizeof(values));
 	MemSet(nulls, 0, sizeof(nulls));
 
-	if (exclusive)
-	{
-		if (status == SESSION_BACKUP_NON_EXCLUSIVE)
-			ereport(ERROR,
-					(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-					 errmsg("non-exclusive backup in progress"),
-					 errhint("Did you mean to use pg_stop_backup('f')?")));
-
-		/*
-		 * Stop the exclusive backup, and since we're in an exclusive backup
-		 * return NULL for both backup_label and tablespace_map.
-		 */
-		stoppoint = do_pg_stop_backup(NULL, waitforarchive, NULL);
-
-		nulls[1] = true;
-		nulls[2] = true;
-	}
-	else
-	{
-		if (status != SESSION_BACKUP_NON_EXCLUSIVE)
-			ereport(ERROR,
-					(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-					 errmsg("non-exclusive backup is not in progress"),
-					 errhint("Did you mean to use pg_stop_backup('t')?")));
+	if (status != SESSION_BACKUP_RUNNING)
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("backup is not in progress"),
+				 errhint("Did you call pg_backup_start()?")));
 
-		/*
-		 * Stop the non-exclusive backup. Return a copy of the backup label
-		 * and tablespace map so they can be written to disk by the caller.
-		 */
-		stoppoint = do_pg_stop_backup(label_file->data, waitforarchive, NULL);
-
-		values[1] = CStringGetTextDatum(label_file->data);
-		values[2] = CStringGetTextDatum(tblspc_map_file->data);
-
-		/* Free structures allocated in TopMemoryContext */
-		pfree(label_file->data);
-		pfree(label_file);
-		label_file = NULL;
-		pfree(tblspc_map_file->data);
-		pfree(tblspc_map_file);
-		tblspc_map_file = NULL;
-	}
+	/*
+	 * Stop the backup. Return a copy of the backup label and tablespace map so
+	 * they can be written to disk by the caller.
+	 */
+	stoppoint = do_pg_backup_stop(label_file->data, waitforarchive, NULL);
 
-	/* Stoppoint is included on both exclusive and nonexclusive backups */
 	values[0] = LSNGetDatum(stoppoint);
+	values[1] = CStringGetTextDatum(label_file->data);
+	values[2] = CStringGetTextDatum(tblspc_map_file->data);
+
+	/* Free structures allocated in TopMemoryContext */
+	pfree(label_file->data);
+	pfree(label_file);
+	label_file = NULL;
+	pfree(tblspc_map_file->data);
+	pfree(tblspc_map_file);
+	tblspc_map_file = NULL;
 
 	/* Returns the record as Datum */
 	PG_RETURN_DATUM(HeapTupleGetDatum(heap_form_tuple(tupdesc, values, nulls)));
@@ -298,7 +214,7 @@ pg_create_restore_point(PG_FUNCTION_ARGS)
 }
 
 /*
- * Report the current WAL write location (same format as pg_start_backup etc)
+ * Report the current WAL write location (same format as pg_backup_start etc)
  *
  * This is useful for determining how much of WAL is visible to an external
  * archiving process.  Note that the data before this point is written out
@@ -321,7 +237,7 @@ pg_current_wal_lsn(PG_FUNCTION_ARGS)
 }
 
 /*
- * Report the current WAL insert location (same format as pg_start_backup etc)
+ * Report the current WAL insert location (same format as pg_backup_start etc)
  *
  * This function is mostly for debugging purposes.
  */
@@ -342,7 +258,7 @@ pg_current_wal_insert_lsn(PG_FUNCTION_ARGS)
 }
 
 /*
- * Report the current WAL flush location (same format as pg_start_backup etc)
+ * Report the current WAL flush location (same format as pg_backup_start etc)
  *
  * This function is mostly for debugging purposes.
  */
@@ -363,7 +279,7 @@ pg_current_wal_flush_lsn(PG_FUNCTION_ARGS)
 }
 
 /*
- * Report the last WAL receive location (same format as pg_start_backup etc)
+ * Report the last WAL receive location (same format as pg_backup_start etc)
  *
  * This is useful for determining how much of WAL is guaranteed to be received
  * and synced to disk by walreceiver.
@@ -382,7 +298,7 @@ pg_last_wal_receive_lsn(PG_FUNCTION_ARGS)
 }
 
 /*
- * Report the last WAL replay location (same format as pg_start_backup etc)
+ * Report the last WAL replay location (same format as pg_backup_start etc)
  *
  * This is useful for determining how much of WAL is visible to read-only
  * connections during recovery.
@@ -402,7 +318,7 @@ pg_last_wal_replay_lsn(PG_FUNCTION_ARGS)
 
 /*
  * Compute an xlog file name and decimal byte offset given a WAL location,
- * such as is returned by pg_stop_backup() or pg_switch_wal().
+ * such as is returned by pg_backup_stop() or pg_switch_wal().
  *
  * Note that a location exactly at a segment boundary is taken to be in
  * the previous segment.  This is usually the right thing, since the
@@ -470,7 +386,7 @@ pg_walfile_name_offset(PG_FUNCTION_ARGS)
 
 /*
  * Compute an xlog file name given a WAL location,
- * such as is returned by pg_stop_backup() or pg_switch_wal().
+ * such as is returned by pg_backup_stop() or pg_switch_wal().
  */
 Datum
 pg_walfile_name(PG_FUNCTION_ARGS)
@@ -646,81 +562,6 @@ pg_wal_lsn_diff(PG_FUNCTION_ARGS)
 }
 
 /*
- * Returns bool with current on-line backup mode, a global state.
- */
-Datum
-pg_is_in_backup(PG_FUNCTION_ARGS)
-{
-	PG_RETURN_BOOL(BackupInProgress());
-}
-
-/*
- * Returns start time of an online exclusive backup.
- *
- * When there's no exclusive backup in progress, the function
- * returns NULL.
- */
-Datum
-pg_backup_start_time(PG_FUNCTION_ARGS)
-{
-	Datum		xtime;
-	FILE	   *lfp;
-	char		fline[MAXPGPATH];
-	char		backup_start_time[30];
-
-	/*
-	 * See if label file is present
-	 */
-	lfp = AllocateFile(BACKUP_LABEL_FILE, "r");
-	if (lfp == NULL)
-	{
-		if (errno != ENOENT)
-			ereport(ERROR,
-					(errcode_for_file_access(),
-					 errmsg("could not read file \"%s\": %m",
-							BACKUP_LABEL_FILE)));
-		PG_RETURN_NULL();
-	}
-
-	/*
-	 * Parse the file to find the START TIME line.
-	 */
-	backup_start_time[0] = '\0';
-	while (fgets(fline, sizeof(fline), lfp) != NULL)
-	{
-		if (sscanf(fline, "START TIME: %25[^\n]\n", backup_start_time) == 1)
-			break;
-	}
-
-	/* Check for a read error. */
-	if (ferror(lfp))
-		ereport(ERROR,
-				(errcode_for_file_access(),
-				 errmsg("could not read file \"%s\": %m", BACKUP_LABEL_FILE)));
-
-	/* Close the backup label file. */
-	if (FreeFile(lfp))
-		ereport(ERROR,
-				(errcode_for_file_access(),
-				 errmsg("could not close file \"%s\": %m", BACKUP_LABEL_FILE)));
-
-	if (strlen(backup_start_time) == 0)
-		ereport(ERROR,
-				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("invalid data in file \"%s\"", BACKUP_LABEL_FILE)));
-
-	/*
-	 * Convert the time string read from file to TimestampTz form.
-	 */
-	xtime = DirectFunctionCall3(timestamptz_in,
-								CStringGetDatum(backup_start_time),
-								ObjectIdGetDatum(InvalidOid),
-								Int32GetDatum(-1));
-
-	PG_RETURN_DATUM(xtime);
-}
-
-/*
  * Promotes a standby server.
  *
  * A result of "true" means that promotion has been completed if "wait" is